Bath and process for the electrodeposition of nickel and nickel-cobalt alloys



United States Patent 3,274,079 BATH AND PROCESS FOR THE ELECTRODEPOSI- OF NICKEL AND NICKEL-COBALT AL- Frank Passal, Detroit, Mich., assignor, by mesne assignments, to M & T Chemicals Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed July 19, 1962, Ser. No. 211,128 14 Claims. (Cl. 20443) The present invention is directed to novel baths and processes for electrodepositing nickel and nickel-cobalt alloys.

Watts-type baths, which contain nickel sulfate, nickel chloride, and boric acid are Widely used for nickel plating. Although these baths are satisfactory in many respects, they have the following disadvantages: (1) the bath pH tends to rise on electrolysis and requires frequent adjustment; (2) certain metallic impurities, such as iron, tend to precipitate as basic salts when the pH exceeds about 3.8 electrometric, resulting in pitting, decrease in deposit luster, clogging of anode bags and filters, etc.; (3) if insufiicient anode area is used resulting in too high anode current densities, chlorine is evolved at the anodes and it is corrosive, a health hazard, and may destroy effectiveness of brightening additives; and (4) the use of insoluble anodes for certain electroforming etc. purposes, or as conforming anodes to increase deposition of nickel in recesses of articles, is practically impossible due to chlorine evolution, at such anodes.

Nickel plating baths for special purposes and generally more limited use, include the high chloride type, the fiuoborate type, and the sulfarnate type. The latter two baths are generally more expensive than the Watts-type baths. In most of the nickel plating baths it is necessary to incorporate chloride ion in order to maintain adequate anode corrosion control. Some of the baths require critical pH control and frequent adjustment of pH to compensate for a rather rapid increase in pH during electrolysis. Other baths such as the fiuoborate and sulfamate type require special operating conditions of temperature, pH, etc., to minimize decomposition or hydrolysis of the anions such as BF or NH SO Prior art fluoridecontaining baths usually contained complex fluoanions such as fiuoborate or silicofluoride, or contained boric acid in addition to fluoride which resulted in the complexing of the fluoride with boric acid in solution to form fiuoborate anions. U.S. Patent 2,436,690 discloses a plating bath containing nickel sulfate, at least one-third of the nickel as the chloride, and fluoride added in the form of a number of specified fluoride salts. It does not appear that this bath has had any commercial success; and this may be because (a) it is subject to rapid fluctuation in pH during electrolysis; (b) the electrolyte is highly corrosive; and (c) the limited solubility of certain of the salts used, including sodium fluoride or nickel fluoride, imposes problems.

Various prior art techniques for the electrodeposition of nickel-cobalt alloys, including use of baths of the Watts type, or the sulfamate type have been tried; but such baths have been undesirably characterized by many of the defects hereinbefore noted.

An object of this invention is to provide novel baths for the eleotrodeposition of nickel and nickel-cobalt alloys. Another object of this invention is to provide improved processes for the electrodeposition of nickel and nickel- PatentedSept. 20, 1966 cobalt alloys. Another object of this invention is to provide novel compositions of matter for making up and for maintaining aqueous nickel and nickel-cobalt alloy electrolytic plating baths. It is another object of this invention to provide a process for obtaining nickel or nickel-cobalt coatings which are fine-grained, and ductile and which may be dull, semi-bright, or brilliant. Other objects will be apparent to those skilled in the art on inspection of the following description.

In accordance with certain of its aspects, the process of this invention for electrodepositing anickel plate or coating (including nickel-cobalt alloy plate or coating) may comprise eleetrodepositing said nickel plate or coating from an aqueous bath consisting essentially of the following ions in the indicatedpreferred quantities:

TABLE I Ion Minimum Maximum Preferred (g-l (al (5/ Nickel Ni++ 10. 5 73 20. 9-52. 2 Ammonium NH 2. 43 36. 5 9. 7-14. 5 Sulfate SO 17.0 120.0, 34.1 8.0 Fluoride F- 2. 57 38. 5 10. 3-15. 4

Where it is desired to produce a coating of a nickelcobalt alloy, the aqueous bath may consist essentially of the following ions in the indicated preferred quantities:

TABLE II Ion Minimum Maximum Preferred (al -l Nickel Ni++ l0. 5 73 20. 9-52. 2 Cobalt C0++ 0.21 19.0

Ammonium NH4 2. 43 17. 0

Sulfate S04 17.3 150 Fluoride F- 2. 57 18. 0

TABLE III.-NICKEL DEPOSITION Broad Preferred B ath Range Range (g-f (EL/ Nickel sulfate 50-350 -250 Ammonium fluoride.-- 5-75 20-30 pH electrometrie 4. 5-6 5. 3-5. 7 Temperature, C 35-65 35-65 TABLE IV.NICKEL-COBALT DEPOSITION Broad Preferred Bath Range Range (al (g-/ Nickel sulfate 50-350 100-250 Cobalt sulfate 1-90 Ammonium fluoride 5-35 20-30 pH electrometrie. 4. 5-6 5. 3-5. 7 35-65 35-65 Temperature, C

The preferred range of cobalt sulfate may depend upon the particular alloy to be plated and the operating conditions chosen to give desired properties in the deposit. It is a particular feature of this invention that when the amounts of the components are properly balanced as disclosed in the above tables, there will be no undesirable precipitation of materials including cobalt fluoride, nickel ammonium sulfate, or nickel fluoride.

The baths specified are operative over a very wide range of current densities. The upper limiting current density at the cathode is remarkably high even at relatively low nickel or low nickel-cobalt metal ion contents. Typically the bath can be operated at a cathode current density of 1-15 amps./dm. and at an anode current density between 1-3 amps/dmF. Specific values may be varied. Both anode and cathode current efficiencies attainable are high, in the order of 93% to 99+%. The bath will function satisfactorily over a wide range of temperatures; a preferred temperature range is 35 C.-65 C.

During electrolysis, the pH range of the baths may be remarkably constant and may require practically no adjustment during long periods of electrolysis. The bath tends to maintain an equilibrium pH of about 5.5 to 5.7. When attempts were made to operate the baths at pH values substantially below 5 electrometric, i.e. within the range of 2 to 4.5, it was found that the pH of the bath immediately began to rise until it reached an equilibrium at about 5.5 to 5.7. The explanation for this is believed to be that at the lower pH values, the anode current efficiency is substantially higher than the cathode current efliciency. This results in liberation of hydrogen at the cathode and a resulting rapid increase of hydroxyl ion concentration, until the equilibrium pH is attained. Baths have been operated in life tests at relatively high currents per unit volume of bath for periods as long as four weeks without any pH adjustment whatsoever.

If, after very long electrolysis, the pH eventually rises to a value a few tenths of a pH unit over 5.7, it can be easily brought down to within the preferred 5.3 to 5.7 range by very small additions of dilute sulfuric acid. The baths of this invention are far better buffered than Watts baths between pH values of 2 and 6 as determined by titration curves; but because the cathode current efliciency drastically decreases with lowering pH, this results in rapid hydroxyl ion build-up thus making the practical range between pH 5 and 6.

Because of the unusual stability of the bath, the only controls necessary during operation are occasional analysis for nickel (or nickel and cobalt) and also for the ammonium ion content. The ammonium ion content is determined by distilling ammonia into standard acid from alkaline solution and calculating the ammonium content from the titrations. The fluoride content can be calculated from the ammonium content.

When using baths for electroplating, they become contaminated with metallic impurities. The baths of this invention are relatively insensitive to metallic impurities. Iron which precipitates out easily in a Watts bath at pH values over 4.0 does not precipitate from the baths of this invention in the pH range utilized. This eliminates the problems encountered in Watts and other baths due to precipitation of basic iron compounds. It is a feature of the baths of this invention that they are much less corrosive and accordingly they do not readily dissolve metals which might interfere with operation of the bath.

In Tables III and IV, the bath components are noted as nickel sulfate, cobalt sulfate, and ammonium fluoride, respectively. In the ionized electrolytes, these compounds dissociate and the actual baths contain the equivalent nickel ions, cobalt ions, ammonium ions, sulfate ions, and fluoride ions. When using these baths for electroplating with soluble anodes, there may be little, if any, need to replace the original bath components for long periods of time due to the excellent balance of anode and cathode current efliciencies. Eventually some additions may be made to replace losses due to dragout. These baths may also be operated with insoluble anodes such as carbon, or with a combination of soluble and insoluble anodes, in which case the metal depleted by plating must be replaced. Although the bath components may be preferably added to the bath (during make-up or maintenance) in the form of nickel sulfate, cobalt sulfate, and ammonium fluoride (the latter most economically in the form of an aqueous concentrate), it may be possible to use equivalent compounds which dissociate in the electrolyte to yield the desired ions and which do not introduce undesirable components into the bath. Such compounds may include sulfuric acid, hydrofluoric acid, ammonium hydroxide, nickel carbonate, cob-altous carbonate, etc.

The nickel and the cobalt-nickel deposits obtained from my baths are ductile and fine-grained. The internal stress of the deposit is tensile but is generally lower than that obtained from equivalent deposits from Watts and fluobor-ate type baths. The stress can be reduced and even made compressive by the use of suitable additives in the bath. The normally fine-grain deposits obtained can be brightened and refined in grain size by additions of additives such as saccharin; sodium 1,3,6-naphthalenetrisulfonate; coumarin; etc. Coumarin (which is rapidly consumed in a Watts bath, making it diflicult to maintain a uniform fine-grain deposit over a wide current density range without frequent replenishment additions) has a much lower rate of consumption in the baths of this invention. It is possible to obtain lustrous semi-bright nickel deposits which are suitable for many purposes, per se, and are also suitable as the lower layer of duplex nickel deposits where the outer layer is a brilliant nickel deposit. Utilizing suitable combinations of primary and secondary nickel brighteners sometimes in conjunction with auxiliary brighteners, it is possible to obtain brilliant ductile deposits from these baths.

A wide range of nickel-cobalt alloys may be deposited from the cobalt sulfate containing baths. These alloys may be ductile, fine-grained, and uniform in appearance. The baths may also be responsive to additives which result in deposits having a decreased grain size and increased luster. Nickel cobalt alloys of varied ratio are deposited dependent upon the bath utilized. With nickelcobalt baths, the ratio of nickel to cobalt in the deposit may depend on the absolute and relative quantities of these metals in the bath, the cathode current density, the bath temperature, the degree of agitation, the pH, etc.

Wetting agents such as sodium lauryl sulfate, sodium lauryl ether sulfate, and sodium Z-ethylhexyl sulfate may be useful in the nickel and nickel-cobalt containing baths. Agitation of the cathode or catholyte may be effected by mechanical movement of the cathode or by air agitation of the electrolyte.

Since the baths of this invention are free of chloride and boric acid, both of which produce deleterious effects on chromium plating baths, they are more suitable than the Watts type baths for nickel plating preceding chromium plating. If, due to inadequate rinsing, small quantities of the nickel plating baths of this invention were carried over on racks, parts etc. into the chromium plating baths, particularly of the mixed radical catalyst of the SO -SiF type, no harmful effects will occur. (If chloride from a nickel plating bath enters a chromium plating bath it is difficult or expensive to remove by such treatments as high current density electrolysis or precipitation with silver salts. Boric acid on the other hand is practically impossible to remove once it enters the chromium plating bath. Both chloride and boric acid may cause increased etching, hazy deposits and other harmful effects.)

For the purpose of giving those skilled in the art a better understanding of my invention, illustrative specific examples are set forth in Table V in which the aqueous baths and conditions used are specified. The nickel (Examples 1-2, 56) and nickel-cobalt (Examples 3-4) alloys were deposited on clean copper cathodes. Either air agitation or moving cathode bar agitation was used 6 I claim: 1. The process for electrodepositing a nickel plate by passing a current from an anode to a cathode to be plated which comprises electrodepositing said nickel plate from in all the examples. 5 an aqueous bath consisting essentially of operative TABLE V Example N0. Bath Nickel sulfate, g./l 110 250 97. 5. 110 110 250 Cobalt sulfate, g./1. 83 10 Ammonium fluoride, 18 20 20 28 pH electromctric 5.5 5.6 5.6 5.5 5.5 5.6 Temperature, C 55 5 55 60 55 55 Anode current density, amps./dm. 2.0 1. 5-2. 0 2.0 2.0 1. 5 1. 5 Cathode current density, amps/dmfl. 2. 0-10 5. 0 3.0 5. 0 4. 0 4. 0 Nickel saccharinate, g./l 4 4 4 Coumarin,g./l 0.1

The nickel deposits obtained from baths 1 and 2 were amounts of 10.5 to 73 g./l. nickel ion Ni++, 2.43 to 36.5 fine-grained, uniform, lustrous, ductile nickel deposits. g./l. ammonium ion NH 17.0 to 120 g./l. sulfate ion The nickel-cobalt alloy deposit from bath 3 was a beauti- 80 and 2.57 to 38.5 g./l. fluoride ion F-. ful highly lustrous, uniform, ductile nickel-cobalt alloy 2. The process for electrodepositing a nickel plate by which contained by analysis 33.9% nickel and 66.1% passing a current from an anode to a cathode to be plated cobalt. The nickel-cobalt alloy deposit obtained from 30 which comprises electrodepositing said nickel plate from bath 4 Was a beautiful lustrous, uniform, fine-grained and an aqueous bath consisting essentially of operative ductile nickel-cobalt alloy. The nickel deposit obtained amounts of 50-350 g./l. nickel sulfate and 5-75 g./l. from bath 5 was a uniform, fine-grained, dull-satiny, ducammonium fluoride. tile nickel deposit. The nickel deposit obtained from 3. The process for electrodepositing a nickel plate by bath 6 was a beautifully uniform fine-grained, leveled, ducpassing a current from an anode to a cathode to be plated tile nickel deposit. which comprises electrodepositing said nickel plate from The baths specified herein have many advantages over an aqueous bath consisting essentially of operative those known to the art. They are relatively inexpensive. amounts of 100-250 g./l. nickel sulfate and 20-30 g./l. Very high plating speeds i.e. high cathode current densiammonium fluoride. ties may be used. When using soluble anodes it is a great 4. The process for electrodepositing a nickel plate by advantage that the anode current efliciency and cathode passing a current from an anode to a cathode to be plated current efliciency are balanced as is true of systems utilizaccording to claim 1 wherein said bath has an electroing the bath of the instant invention. Anode corrosion is metric pH of 4.5-6 and a temperature of 35 C.65 C. excellent despite the absence of chloride ion which is 5. The process for electrodepositing a nickel-cobalt algenerally considered necessary for optimum anode corloy plate by passing a current from an anode to a cathode rosion. Although the system utilizes the fluoride ion, the to be plated which comprises electrodepositing said bath does not have a pronounced corrosive action either nickel-cobalt alloy plate from an aqueous bath consisting on glass or metals. The nickel electrodeposits from the essentially of operative amounts of 10.5 to 73 g./l. nickel baths of this invention may be deposited on the usual basis ion Ni++, 0.21 to 19.0 g./l. cobalt ion Co++, 2.43 to 17.0 metal such as iron, copper, brass, bronze, etc. Suitable g./l. ammonium ion NH 17.3 to 150 g./l. sulfate ion nickel deposits may be electrodeposited on zinc where an 80 and 2.57 to 18.0 g./l. fluoride ion F. adherent coating of another metal or alloy which does not 6. The process for electrodepositing a nickel-cobalt alin time diffuse into the zinc, is applied before nickel loy plate by passing a current from an anode to a cathode plating. to be plated which comprises electrodepositing said The baths of this invention are particularly useful for nickel-cobalt alloy plate from an aqueous bath consisting plating zinc and zinc-alloys since (in contrast to the highly 5 essentially of operative amounts of 50350 g./l. nickel corrosive chloride-containing, lower pH baths of the prior Sulfate, l-90 g./l. cobalt sulfate, and 5-35 g./l. amart) the system of this invention has little tendency to monium fluoride. attack these basis metals. This gives a lower tendency 7. The process for electrodepositing a nickel-cobalt alto build up zinc as a contaminant in the bath electrolyte loy plate by passing a current from an anode to a cathode resulting in more lustrous deposits and better receptivity to be plated which comprises electrodepositing said for chromium in low current density areas. nickel-cobalt alloy plate from an aqueous bath consisting Nickel deposited from the specified baths has a wide essentially of operative amounts of 100-250 g./l. nickel variety of uses. The nickel-cobalt alloys are useful in sulfate, l-90 g./l. cobalt sulfate, and 2030 g./l. amthe industrial field, e.g. those having special magnetic monium fluoride. properties for memory devices and similar applications. 8. An aqueous electrolytic bath for the deposition of Both the nickel and nickel-cobalt baths may be used in nickel plate consisting essentially of operative amounts of barrel plating. They are also useful in obtaining indus- 10.5 to 73 g./l. nickel ion Ni++, 2.43 to 36.5 g./l. amtrial finishes where a tough, durable, ductile deposit is monium ion NH 17.0 to 120 g./l. sulfate ion 80 and desired at a low cost. The baths of this invention may be 2.57 to 38.5 g./l. fluoride ion F. used for electrorefining and electrowinning. 9. An aqueous electrolytic bath for the deposition of As many embodiments of this invention may be made nickel plate consisting essentially of operative amounts of without departing from the spirit and scope thereof, it is 50350 g./l. nickel sulfate and 5-75 g./l. ammonium to be understood that the invention includes all such modifluoride. fications and variations as come within the scope of the 10. An aqueous electrolytic bath for the deposition of appended claims. 75 nickel plate according to claim 8 wherein said bath has 7 an electrometric pH of 4.5-6 and a temperature of 35 C.65 C.

11. A novel composition of matter consisting essentially of 50350 parts by Weight of nickel sulfate and 5- 75 parts by Weight of ammonium fluoride.

12. An aqueous electrolytic bath for the deposition of nickel-cobalt plate consisting essentially of 10.5 to 73 parts by Weight of nickel ion Ni++, 0.21 to 19.0 parts by weight of cobalt ion Co++, 2.43 to 17.0 parts by Weight of ammonium ion NHJ, 17.3 to 150 parts by weight of sulfate ion 80 2.57 to 18.0 parts by weight of fluoride ion F 13. A novel composition of matter consisting essentially of 50350 parts by weight of nickel sulfate, 190 parts by weight of cobalt sulfate, and 5-35 parts by Weight of ammonium fluoride.

References Cited by the Examiner UNITED STATES PATENTS 2,436,690 2/1948 Du ROSe 20449 2,519,858 8/1950 Spiro et a1 20443 2,728,720 12/1955 DeLong 204-49 JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, Examiner.

G. KAPLAN, Assistant Examiner. 

1. THE PROCESS FOR ELECTRODEPOSITING A NICKEL PLATE BY PASSING A CURRENT FROM AN ANODE TO A CATHODE TO BE PLATED WHICH COMPRISES ELECTRODEPOSITING SAID NICKEL PLATE FROM AN AQUEOUS BATH CONSISTING ESSENTIALLY OF OPERATIVE AMOUNTS OF 10.5 TO 73 G./L. NICKEL ION NI++, 2.43 TO 36.5 G./L. AMMONIUM ION NH4+, 17.0 TO 120 G./L. SULFATE ION SO4=, AND 2.57 TO 38.5 G./L. FLUORIDE ION F-.
 5. THE PROCESS FOR ELECTRODEPOSITING A NICKEL-COBALT ALLOY PLATE BY PASSING A CURRENT FROM AN ANODE TO A CATHODE TO BE PLATED WHICH COMPRISES ELECTRODEPOSITING SAID NICKEL-COBALT ALLOY PLATE FROM AN AQUEOUS BATH CONSISTING ESSENTIALLY OF OPERATIVE AMOUNTS OF 10.5 TO 73 G./L. NICKEL ION NI++, 0.21 TO 19.0 G./L. COBALT ION CO++, 2.43 TO 17.0 G./L. AMMONIUM ION NH4+, 17.3 TO 150 G./L. SULFATE ION SO4=, AND 2.57 TO 18.0 G./L. SULFATE ION 